UPSC Prelims 2015·CSAT·Logical Reasoning·Coding Decoding

Consider the following matrix: 3 8 10 2 ? 1 6 56 90 2 20 0 What is the missing number at '?' in the matrix?

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Last updated 8 Jul 2026, 4:39 pm IST
  1. A5Correct
  2. B0
  3. C7
  4. D3

Explanation

The pattern in the matrix is that the number in the second row is obtained by multiplying the corresponding number in the first row by (that number minus 1).

Let's verify this pattern for the given columns:

  1. For 3 and 6: 3 * (3 - 1) = 3 * 2 = 6. (Matches)
  2. For 8 and 56: 8 * (8 - 1) = 8 * 7 = 56. (Matches)
  3. For 10 and 90: 10 * (10 - 1) = 10 * 9 = 90. (Matches)
  4. For 2 and 2: 2 * (2 - 1) = 2 * 1 = 2. (Matches)
  5. For 1 and 0: 1 * (1 - 1) = 1 * 0 = 0. (Matches)

Now, apply this pattern to find the missing number (let's call it 'x') where the second row number is 20: x * (x - 1) = 20

Let's test the options: A) If x = 5: 5 * (5 - 1) = 5 * 4 = 20. This matches the pattern. B) If x = 0: 0 * (0 - 1) = 0 * -1 = 0. (Does not match 20) C) If x = 7: 7 * (7 - 1) = 7 * 6 = 42. (Does not match 20) D) If x = 3: 3 * (3 - 1) = 3 * 2 = 6. (Does not match 20)

Therefore, the missing number is 5.

The final answer is A

Logical Reasoning: Consider the following matrix: 3 8 10 2 ? 1 6 56 90 2 20 0 What is the missing number at '?' in the matrix?
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